Coding device and method, and decoding device and method

ABSTRACT

Conventionally, to code a digitized image signal, a corresponding quantity of information is allocated to an edge part for carrying out coding, and therefore reduction in the quantity of information is limited, deteriorating the coding efficiency. 
     Thus, an evaluation section of an encoder evaluates the characteristics (strength of correlation between pixels) of an image using a predetermined evaluation function, and decides a transmission pixel in accordance with the characteristics, consequently deciding a random scan order. A differential coding section differentially codes the image on the basis of the scan order decided by the evaluation section. A multiplexing section multiplexes the differential coding output from the differential coding section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 09/574,616, filed May 18, 2000, which is a continuation ofInternational Application PCT/JP99/05166 having an international filingdate of 21 Sep. 1999.

TECHNICAL FIELD

This invention relates to a coding device and method for coding images,and a decoding device and method for decoding coded data.

BACKGROUND ART

Conventionally, when coding digitized television signals, peripheralinformation of pixels to be transmitted is used for coding for thefollowing reason. That is, an image generally has strongauto-correlation in a neighboring area, and it is more efficient to usedata of the neighboring area in case of compression.

Microscopically, however, a strong correlation is found in a flat partwhere no signal change occurs while little correlation can be found inan edge part of an image where the signal abruptly changes.

In such case, conventionally, the strength of correlation is fullyutilized for coding in a part where a strong correlation is found, andin an edge part, a corresponding quantity of information is allocatedfor carrying out coding, or coding is carried out within such a rangethat a visual masking effect can be obtained.

Meanwhile, in the conventional coding, a corresponding quantity ofinformation is allocated for carrying out coding in an edge part of animage. Therefore, the reduction in the quantity of information islimited, thus deteriorating the coding efficiency.

DISCLOSURE OF THE INVENTION

In view of the foregoing status of the art, it is an object of thepresent invention to provide a coding device and method which enablesreduction in the quantity of information and improvement in the codingefficiency of a signal value, by finding a pixel of the highestcorrelation even in an edge part and carrying out coding through randomscan.

It is another object of the present invention to provide a decodingdevice and method which enables easy decoding of an image that is codedand transmitted in a random scan order in accordance with thecharacteristics of the image.

A coding device according to the present invention includes: anevaluation section for deciding, on the basis of the characteristics ofan image signal having a plurality of pixel data, the coding order forthe plurality of pixel data; and a coding section for coding theplurality of pixel data in the order decided by the evaluation section.

A decoding device according to the present invention is adapted fordecoding, from a plurality of coded pixel data generated by coding animage signal made up of a plurality of pixel data having a predeterminedorder in an order based on the characteristics thereof, the plurality ofpixel data having the predetermined order. The decoding device includes:a position data extraction section for extracting position data includedin each of the plurality of coded pixel data; a level data extractionsection for extracting level data included in each of the plurality ofcoded pixel data; and a conversion section for converting the level dataof the plurality of coded pixel data to the predetermined order on thebasis of the position data.

A coding method according to the present invention includes: a step ofdeciding, on the basis of the characteristics of an image signal havinga plurality of pixel data, the coding order for the plurality of pixeldata; and a step of coding the plurality of pixel data in the orderdecided at the step of deciding.

A decoding method according to the present invention includes: a step ofextracting, on the basis of an image signal having a plurality of pixeldata, the coding order for the plurality of pixel data; and a step ofdecoding the plurality of pixel data in the order extracted at the stepof extracting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an image processingsystem, which is an embodiment of the present invention.

FIG. 2A is a signal distribution view showing biased distribution of atypical image signal in a color space of an RGB calorimetric system.

FIG. 2B is an information distribution view in an address space.

FIG. 3A is a view for explaining the concept of conventional scan.

FIG. 3B is a view for explaining the concept of scan according to thepresent invention.

FIG. 4 is a view showing the format of pixel information.

FIG. 5 is a block diagram showing the detailed structure of an encoderin a coding device of the image processing system.

FIG. 6 is a flowchart for explaining optimization processing of thepixel transmission order carried out by the encoder shown in FIG. 5.

FIG. 7 is a block diagram showing the detailed structure of anevaluation section constituting the encoder.

FIG. 8 is a block diagram showing the detailed structure of anevaluation function unit constituting the evaluation section.

FIG. 9 is a block diagram showing the detailed structure of acorrelation discrimination unit constituting the evaluation functionunit.

FIG. 10 is a block diagram showing the structure of a decoder in areceiving device of the image processing system.

FIG. 11 is a block diagram showing another specific example of theencoder shown in FIG. 5.

FIG. 12 is a view showing four pixels of a 2×2-pixel block used forexplaining decimation processing carried out by the encoder shown inFIG. 11.

FIGS. 13A, 13B, 13C and 13D are views showing four patterns ofdecimation performed on the four pixels shown in FIG. 12.

FIG. 14 is a block diagram showing another specific example of thedecoder shown in FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will now be describedwith reference to the drawings. In this embodiment, an image processingsystem 1 as shown in FIG. 1 is employed. The image processing system 1includes a coding device 2 for coding digitized pixel information andoutputting coded data, a transmission medium 10 for transmitting thecoded data outputted from the coding device 2, and a decoding device 6for receiving the coded data transmitted by the transmission medium 10and decoding the received data.

With respect to a part where raster scan is disadvantageous to imagecorrelation such as an edge part of an image of a typical televisionsignal, the coding device 2 searches for another candidate havingstronger image correlation so as to carry out coding, rather than codingpixel information in the disadvantageous direction. In short, instead ofemploying a regular coding order, pixel information as a coding targetis sequentially decided in a random direction, which is different from araster scan direction decided on the basis of the correlation of pixelinformation, in accordance with the characteristics and signaldistribution of the image.

In a typical color image signal, the signal level distribution of theimage is biased to a certain extent as shown in FIG. 2A, for example, ina color space of an RGB colorimetric system. On the other hand, whenexpressed in an address space, the image signal is uniformly distributedin a space such as a macroblock as shown in FIG. 2B. Thus, the codingdevice 2 splits an image signal having a plurality of pieces of pixelinformation into a plurality of macroblocks, and coded and transmitslevel information of each pixel information in the macroblocks andposition information in accordance with the characteristics and signaldistribution of the image signal.

The concept of the scan system according to the coding method of thepresent invention, employed by the coding device 2, will now bedescribed with reference to FIG. 3. In the case of block coding withrespect to a block of a given size, pixel information in the block isusually coded in a raster scan order as shown in FIG. 3A. On thecontrary, in the coding method of the present invention employed by thecoding device 2, an optimum macroblock area is set so as to search forthe next pixel information to be coded, and the pixel information iscoded in the optimum order within the macroblock. Therefore, as shown inFIG. 3B, the pixel information in each macroblock is coded andtransmitted in a random order. The optimum order for coding the pixelinformation may be decided in an entire frame or in an entire field.

In the coding device 2 of FIG. 1, digital pixel information inputtedfrom an input terminal IN_(T) in a raster scan order is stored inmemories 3 a and 3 b. These memories 3 a and 3 b have a bank switchingstructure in which pixel information of each macroblock is read out fromone memory while pixel information of each macroblock is written intothe other memory. Therefore, a macroblock read section 4 can read outpixel information of each macroblock from the memories 3 a and 3 b atdifferent timing.

The pixel information read out for each macroblock by the macroblockread section 4 is supplied to an encoder 5. The encoder 5 optimizes thetransmission order for the pixel information in the macroblock andremoves the redundancy, thus outputting coded pixel data. The codedpixel data from the encoder 5 is outputted to the transmission medium 10via an output terminal OUT_(T).

The coding by the encoder 5 will now be described.

First, an example of the format of pixel information is shown in FIG. 4.As pixel information P, signal level information L of the pixel andposition information A of the pixel are used. As the signal levelinformation L of the pixel, R, G and B primary colors are considered inthis case, though a luminance signal Y, a blue color-difference signalCb and a red color-difference signal Cr may be considered. As theposition information A of the pixel, address positions X and Y of atarget pixel on the two-dimensional coordinate are considered.

The encoder 5 splits each pixel information P in the macroblock intofive components R, G, B, X and Y as shown in FIG. 4, and codes andtransmits the components. The encoder 5 finds the difference betweenpixel information Ps (Rs, Gs, Bs, Xs, Ys) and pixel candidate Pn (Rn,Gn, Bn, Xn, Yn) to be coded and transmitted next, and finds the sum E ofabsolute values of the difference as expressed by an equation (1). Usingthe sum E of absolute values as an evaluation value, the encoder 5decides the next pixel information Pn to be coded and transmitted sothat the minimum evaluation value is obtained.E=|Rn−Rs|+|Gn−Gs|+|Bn−Bs|+|Xn−Xs|+|Yn−Ys|  (1)

After deciding the transmission order using the evaluation function ofthe equation (1), the encoder 5 differentially codes the next pixelinformation Pn to be transmitted, and outputs the coded pixel data tothe transmission medium 10. The encoder 5 will be later described indetail.

As the transmission medium 10, a disc-like or tape-like recording mediummay be used as well as a communication channel such as a network.

The coded pixel data transmitted through the transmission medium 10 isinputted to the decoding device 6 via an input terminal IN_(R). Adecoder 7 decodes the address information X and Y, and stores decodedvalues of the signal level information at positions based on the addressinformation X and Y in memories 9 a and 9 b having a band switchingstructure. Then, a macroblock read section 8 reads out the signal levelinformation in the macroblock in the raster order from the memories 9 aand 9 b, and outputs the signal level information from an outputterminal OUT_(R).

The structure and operation of the encoder 5 and the decoder 7 will nowbe described in detail.

The details of the structure of the encoder 5 are shown in FIG. 5. Thisencoder 5 includes an evaluation section 13 for evaluating thecharacteristics (strength of correlation between pixels) of an imagesignal using the evaluation value E of the equation (1) and for decidingthe order for coding a plurality of pieces of pixel information in themacroblock in accordance with the characteristics, a differential codingsection 16 for differentially coding the plurality of pieces of pixelinformation in the macroblock in the order decided by the evaluationsection 13, and a multiplexing section 17 for multiplexing thedifferential coding output from the differential coding section 16.

The encoder 5 also has a memory 11 so as to store into the memory 11 thesignal level information of the pixel information read out from thememories 3 a and 3 b for each of the components R, G and B. The encoder5 also has an address counter 12 so as to count the address informationX and Y of the signal level information by the address counter 12.

In the encoder 5, the signal level information from the memory 11 andthe address information from the address counter 12 are read out, andthe processing for optimizing the transmission order for the pixelinformation, that is, the processing for deciding the next pixelinformation to be transmitted, is carried out in accordance with theprocedures shown in FIG. 6.

First, at step S1, the encoder 5 decodes initial transmission pixelinformation Ps. Although an arbitrary value is used in this case, thevalue may be decided by an optimum method based on a predeterminedalgorithm.

Next, at step S2, the encoder 5 selects a pixel information candidate Pnthat should be transmitted next to the initial transmission pixelinformation Ps. The processing for selecting the transmission pixelinformation candidate Pn is carried out with respect to pixelinformation which is determined as not being transmitted yet at step S3,and is not carried out with respect to pixel information which isdetermined as being already transmitted.

Then, at step S4, the encoder 5 uses the evaluation section 13 toevaluate the correlation with respect to the pixel information candidatePs using the evaluation function of the equation (1). The equation (1)is adapted to find the difference between the pixel information Ps (Rs,Gs, Bs, Xs, Ys) to be transmitted and the pixel information candidate Pn(Rn, Gn, Bn, Xn, Yn) to be transmitted next in the macroblock, and usesthe sum of absolute value of the difference as the evaluation value E.

Subsequently, at step S5, the encoder 5 determines whether theevaluation value E of the evaluation function of the equation (1) is theminimum or not. If the evaluation value E is the minimum value, theprocessing goes to step S6 and the value of pixel information in aminimum value buffer, later described, provided inside the evaluationsection 13 is rewritten. If the evaluation value E is not the minimumvalue, rewrite is not carried out. The encoder 5 repeats the minimumvalue search processing up to this step with respect to all the pixelinformation in the macroblock (step S7).

On completion of the search processing with respect to all the pixelinformation in the macroblock at step S7, the encoder 5 transmits thepixel information in the minimum value buffer as the next pixelinformation to be transmitted (step S8).

By repeating the processing of steps S2 to S8 until all the pixels inthe macroblock are transmitted (step S9), the encoder 5 decides the nextpixel information to be transmitted. As a matter of course, the encoder5 may decide, at this point, the next pixel information to betransmitted and may transmit it at any time.

The principle of the search processing with respect to all the pixels inthe encoder 5 (corresponding to step S7) will now be described using anexemplary hardware structure as shown in FIG. 7.

It is assumed that the hardware structure has a plurality of evaluationfunction units for computing the evaluation function of the equation (1)from the level information R, G, B and the position information X, Y ofthe pixel information so as to find the evaluation value E.

When a clock rate for processing each pixel is used, with respect to npieces of pixel information from an input terminal 21, an evaluationfunction unit 22 _(n−1) repeats calculation of the evaluation value E inaccordance with the evaluation function of the equation (1) for n−1times, and decides pixel information which realizes the minimumevaluation value E, as the pixel to be transmitted next to the initialtransmission pixel information.

An evaluation function unit 22 _(n−2) repeats calculation of theevaluation value E in accordance with the evaluation function of theequation (1) for n−2 times, excluding the two pieces of pixelinformation for which the transmission order is already decided by thecalculation at the evaluation function unit 22 _(n−1), and thus decidesthe third pixel information to be transmitted.

Then, the calculation of the evaluation function of the equation (1) isrepeated for n−3 times, n−4 times, . . . , once, until an evaluationfunction unit 22 ₁ decides the last pixel to be transmitted in themacroblock.

The evaluation function units 22 _(n−1), 22 _(n−2), . . . , 22 ₁ areconnected with transmission flag memories 23 _(n−1), 23 _(n−2), . . . ,23 ₁, respectively, in which a flag indicating “transmission completed”or “transmission not completed” is stored for every 8×8 pixels.

The detailed structure of the evaluation function units 22 _(n−1), 22_(n−2), . . . , 22 ₁ is shown in FIG. 8. On the assumption that thecomponents of the previously transmitted pixel information are referredto as former values (including the initial transmission pixelinformation) while the components of the next pixel information to betransmitted are referred to as latter values (candidate values oftransmission pixel information), the correlations between the formervalues R₁, G₁, B₁, X₁, Y₁, and the latter values R₂, G₂, B₂, X₂, Y₂ arediscriminated by correlation discrimination units 25 _(R), 25 _(G), 25_(B), 25 _(X) and 25 _(Y), respectively. In the correlationdiscrimination unit 25, for example, with respect to R as shown in FIG.9, the difference R₂−R₁, between the former value R₁ and the lattervalue R₂ is found by a difference section 31, and the absolute value ofthe difference |R₂−R₁| is found by an absolute value section 32. Then,the absolute value of the difference |R₂−R₁| and the latter value R₂ areoutputted.

The absolute values of the differences of the respective components fromthe correlation discrimination units 25 _(R), 25 _(G), 25 _(B), 25 _(X)and 25 _(Y) are supplied to an adder 26. The latter values of therespective components are supplied to latches 29 _(R), 29 _(G), 29 _(B),29 _(X) and 29 _(Y).

The addition result obtained by the adder is equal to the evaluationvalue E as follows.|R ₂ −R ₁ |+|G ₂ −G ₁ |+|B ₂ −B ₁ |+|X ₂ −X ₁ |+|Y ₂ −Y ₁|

The addition result is sent to a comparator 28. The comparator 28compares an evaluation value from a minimum value buffer 27 which storesthe minimum evaluation value up to this point, with the currentevaluation value obtained as the result of addition. If the currentevaluation value (addition result from the adder 26) is smaller than theevaluation value stored in the minimum value buffer 27, a reset outputis sent to the minimum value buffer 27 and the latches 29 _(R), 29 _(C),29 _(B), 29 _(X) and 29 _(Y) so as to reset the values of the buffer andlatches. Therefore, in the latches 29 _(R), 29 _(G), 29 _(B), 29 _(X)and 29 _(Y), the pixel information candidate used for calculating a newevaluation value, that is, the latter values R₂, G₂, B₂, X₂, Y₂ arestored, respectively. After the search processing with respect to allthe pixel information in the macroblock is completed, the last pixelinformation Pn (Rn, Gn, Bn, Xn, Yn) stored in the latches 29 _(R), 29_(G), 29 _(B), 29 _(X) and 29 _(Y) is transmitted.

The pixel information Pn (Rn, Gn, Bn, Xn, Yn) thus transmitted from theevaluation section 13 is supplied to subtracters 15 _(R), 15 _(G), 15_(B), 15 _(X), 15 _(Y). The subtracters 15 _(R), 15 _(G), 15 _(B), 15_(X), 15 _(Y) calculate difference values D_(R), D_(G), D_(B), D_(X),D_(Y) between the already transmitted pixel information Ps (Rs, Gs, Bs,Xs, Ys) and the next pixel information to be transmitted Pn (Rn, Gn, Bn,Xn, Yn) stored in latches 14 _(R), 14 _(G), 14 _(B), 14 _(X), 14 _(Y),and send the difference values to differential coders 16 _(R), 16 _(G),16 _(B), 16 _(X), 16 _(Y) of the differential coding section 16,respectively. The differential coders 16 _(R), 16 _(G), 16 _(B), 16_(X), 16 _(Y) differentially code the difference values D_(R), D_(G),D_(B), D_(X), D_(Y), respectively. As a differential coding method,there is employed DPCM for re-quantizing the difference value, or acoding method using Huffman coding with optimization of the frequency ofthe difference value.

The coded values of the differences of the respective components fromthe difference coding section 16 are multiplexed by the multiplexingsection 17 and transmitted to the decoding device 6 through thetransmission medium 10.

The decoder 7 shown in FIG. 1 will now be described in detail withreference to FIG. 10. This decoder 7 carries out the decoding method ofthe present invention. The decoding method is adapted for decoding animage which is coded and transmitted in a random scan order inaccordance with the characteristics of the image. In this method, pixelinformation of the transmitted image is decoded, and the image signal isread out in a raster scan order on the basis of the decoded pixelinformation.

To carry out the decoding method, the decoder 7 includes a splittingsection 42 for splitting the coded value of the difference of the pixelinformation multiplexed in the encoder 5 into coded values ofdifferences of the respective components, a differential decodingsection 43 for decoding the differences from the coded values ofdifferences of the respective components split by the splitting section42, adders 44 and latches 45 constituting a component decoding sectionfor obtaining component values of the pixel information from thedifferential decoding output from the differential decoding section 43,and macroblock memories 46 a and 46 b in which the level information R,G, B of the pixel information is written on the basis of the addressinformation X, Y obtained by the component decoding section and fromwhich the pixel information is subsequently read out in an ordinary scanorder. The address for reading at the macroblock memories 46 a and 46 bis counted by an address counter 47 as an address following the ordinaryscan order.

The following is the flow of operation of the decoder 7. That is, thesplitting section 42 splits the differential coding value of themultiplexed components randomly transmitted thereto from the inputterminal 6, and supplies the split values to differential decoders 43_(R), 43 _(G), 43 _(B), 43 _(X), 43 _(Y) of the differential decodingsection 43, respectively.

The difference values of the respective components decoded by thedifferential decoders 43 _(R), 43 _(G), 43 _(B), 43 _(X), 43 _(Y) aresupplied to the adders 44 _(R), 44 _(G), 44 _(B), 44 _(X), 44 _(Y)constituting the component decoding section, and are added to latchaddition outputs from the latches 45 _(R), 45 _(G), 45 _(B), 45 _(X), 45_(Y). The respective component decoding outputs from the componentdecoding section are supplied to the macroblock memories 46 a and 46 bhaving a bank structure. Since the address counter 47 reads out, byraster scan, the address information used for random scan as describedabove, an image signal that is written in a random scan order isconverted to an image signal in a raster scan order and then outputtedfrom the macroblock memories 46 a and 46 b.

Thus, in the above embodiment, since a pixel of high correlation issearched for so as to carry out coding by raster scan coding withrespect to an edge part or the like where no correlation can be found,the coding efficiency of the signal value is significantly high.Although the quantity of information is increased as address informationwhich is not necessary for raster scan is sent, the quantity ofinformation of the signal value can be reduced to a greater extent andtherefore the coding efficiency is improved as a whole.

In the coding device 2 of the image processing system shown in FIG. 1,an encoder 50 shown in FIG. 11 may be used in place of the encoder 5.The encoder 50 differs from the encoder 5 in that a decimation section51 is provided on the stage before the evaluation section 13.

The decimation section 51 reduces the signal level information andaddress information of the pixel information. The principle of thedecimation section 51 will now be described with reference to FIGS. 12and 13A to 13D. The four pixels of a 2×2-pixel block shown in FIG. 12are taken into consideration, and four patterns of pixel densities ofFIG. 13A to 13D are adaptively employed with respect to the signaldistribution of the four pixels. The four pixels have pixels values a,b, c, d, respectively.

It is now assumed that TH represents a threshold value. In the pattern 1of FIG. 13A, the pixel values are replaced by (a+b+c+d)/4 when |a−b|<TH,|b−c|<TH, |c−d|<TH, |d−a|<TH, |a−c|<TH and |b−d|<TH are all satisfied.In the pattern 2 of FIG. 13B, the pixel values are replaced by (a+c)/2and (b+d)/2 when only |a−b|<TH and |c−d|<TH are satisfied. In thepattern 3 of FIG. 13C, the pixel values are replaced by (a+b)/2 and(c+d)/2 when only |a−c|<TH and |b−d|<TH are satisfied. In the pattern 4of FIG. 13D, the original pixel values are maintained when none of theabove conditions is met.

By using the encoder 50 having this decimation section 51 for the codingdevice, the quantity of information is reduced.

FIG. 14 shows the structure of a decoder 53 which is necessary when theencoder 50 is used. On the image signal read out from the macroblockmemories 46 a and 46 b, interpolation processing using a line memory 54must be performed by a pixel address interpolation section 55. Theinterpolation output is outputted from an output terminal 56.

In the coding device 1, the random scan order may be optimized withrespect to pixels for each macroblock in a frame image, or the randomscan order may be optimized with respect to pixels for each macroblockin a field image. Moreover, a macroblock in the direction of time basemay be used as a unit. The macroblocks need not be sent sequentially andthe difference of the leading address of the macroblocks may be sent.

INDUSTRIAL APPLICABILITY

According to the present invention, since a pixel of high correlation issearched for so as to carry out coding even in an edge part, thequantity of information can be reduced and the coding efficiency of thesignal value can be improved. Also, an image which is coded andtransmitted in a random scan order in accordance with thecharacteristics of the image can be decoded with a simple structure.

1. A decoding device for decoding, from a plurality of coded pixel datagenerated by coding an image signal made up of a plurality of pixel datahaving a predetermined order in an order based on the characteristicsthereof, the plurality of pixel data having the predetermined order, thedevice comprising: a position data extraction section for extractingposition data included in each of the plurality of coded pixel data; alevel data extraction section for extracting level data included in eachof the plurality of coded pixel data; and a conversion section forconverting the level data of the plurality of coded pixel data to thepredetermined order on the basis of the position data.
 2. The decodingdevice as claimed in claim 1, wherein the plurality of coded pixel datais coded in an order based on the characteristics for each predeterminedrange.
 3. The decoding device as claimed in claim 2, wherein thepredetermined range is the same frame or field.
 4. The decoding deviceas claimed in claim 3, wherein the predetermined range is in the samemacroblock in the same frame or field.
 5. The decoding device as claimedin claim 1, wherein the coded pixel data is differentially coded in thepredetermined order, the position data extraction section carries outdifferential decoding, thereby extracting the position data included ineach of the plurality of coded pixel data, and the level data extractionsection carries out differential decoding, thereby extracting the leveldata included in each of the plurality of coded pixel data.
 6. Thedecoding device as claimed in claim 1, wherein the coded pixel data hasthe coding order decided therefor after a part of the plurality of pixeldata having the predetermined order is decimated, the device furthercomprising an interpolation processing section for carrying out pixelinterpolation processing with respect to the pixel data converted to thepredetermined order by the conversion section.
 7. A decoding method fordecoding, from a plurality of coded pixel data generated by coding animage signal made up of a plurality of pixel data having a predeterminedorder in an order based on the characteristics thereof, the plurality ofpixel data having the predetermined order, the method comprising: a stepof extracting position data included in each of the plurality of codedpixel data; a step of extracting level data included in each of theplurality of coded pixel data; and a step of converting the level dataof the plurality of coded pixel data to the predetermined order on thebasis of the position data.
 8. The decoding method as claimed in claim7, wherein the plurality of coded pixel data is coded in an order basedon the characteristics for each predetermined range.
 9. The decodingmethod as claimed in claim 8, wherein the predetermined range is thesame frame or field.
 10. The decoding method as claimed in claim 9,wherein the predetermined range is in the same macroblock in the sameframe or field.
 11. The decoding method as claimed in claim 7, whereinthe coded pixel data is differentially coded in the predetermined order,and wherein at the step of extracting the position data, differentialdecoding is carried out, thereby extracting the position data includedin each of the plurality of coded pixel data, and at the step ofextracting the level data, differential decoding is carried out, therebyextracting the level data included in each of the plurality of codedpixel data.
 12. The decoding method as claimed in claim 7, wherein thecoded pixel data has the coding order decided therefor after a part ofthe plurality of pixel data having the predetermined order is decimated,the method further comprising a step of carrying out pixel interpolationprocessing with respect to the pixel data converted to the predeterminedorder at the conversion step.